Flat side valve for a pump

ABSTRACT

Two confronting relatively movable radial surfaces formed by a stationary pressure part and a movable valve part respectively, have an axially projecting circumferentially continuous shoulder formed on one of the parts and disposed between the surfaces to partition the space between the two parts into an inlet zone and an outlet zone. The valve part is moved axially as a function of fluid flow to by-pass fluid directly across the shoulder into the inlet zone from the outlet zone.

United States Patent Drutchas et al.

[ 1 July 25,1972

54] FLAT SIDE VALVE FOR A PUMP 2,380,783 7/1945 Painter ..4|7 3|0 4 0 68t [72] inventors: Gilbert H. Drutchas, Birnungham; George 23232 21: a]A. Benn, Detroit; Pump B. Spencer,

R alO k,all fM h. 0y 3 o v Primary Examiner-Carlton R. Croyle AsslgneeiTRW Cleveland, Ohio Assistant Examiner-John J. Vrablik [22] Filed: June8 1970 Attorney-Hill, Sherman, Meroni, Gross & Simpson [21] Appl. No.:44,268 [57] ABSTRACT Two confronting relatively movable radial surfacesformed by I U-S. "417/300, 4 1 l 0 a tationary press u-e pan and amovable valve pan respective- 51 lnt. (,l ..F04b 49/00 1y, have anaxially projecting circumferentiany continuous [58] dd 0' Search l 37/]17, fl97; 4l7/53, 300, Shoulder formed on one of the parts and disposedbetween the 417/304 310 surfaces to partition the space between the twoparts into an 6 R f Ct d inlet zone and an outlet zone. The valve partis moved axially [5 1 e erences e as a function of fluid flow to by-passfluid directly across the UNITED STATES PATENTS shoulder into the inletzone from the outlet zone.

3,125,028 3/1964 Rohde ..4l7/300 6 Claims, 8 Drawing Figures 12 III 17IE 14 n .71

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sum 1 or 3 FLAT SIDE VALVE FOR A PUMP BACKGROUND OF THE INVENTION 1.Field of the Invention This invention relates generally to a combinedpump and valving structure, for example, a power steering pump having anintegral flow control valve embodied therein.

2. The Prior Art The prior art in regard to which the present inventionconstitutes an improvement is exemplified by various patents issued tothe same assignee of the present invention such as Clark and DrutchasPat. Nos. 3,200,752 and 3,273,503. In those patents, there is discloseda power steering pump utilizing a stackup of parts and wherein a plateconstituting the outermost part carries a flow control valve.

SUMMARY OF THE INVENTION The present invention is based upon a so-calledflat side valve concept wherein two confronting relatively movableradial surfaces formed by a pressure part and an adjoining valve partare partitioned by a circumferentially continuous shoulder disposedtherebetween in order to provide inner and outer zones. Thus, fluid atpump generated pressure is directed into one of the zones, for example,the innermost zone while the outer zone is vented back to the pumpinlet. It is further contemplated by the present invention that a flowcontrol orifice be formed in the valve part thereby to direct all of thefluid discharged by the pump through the flow control orifice so thatthe valve part may be movable as a function of the pressure drop acrossthe orifice thereby to selectively separate the radial surfaces anddirectly by-pass fluid from the outlet zone across the shoulder to theinlet zone.

It is further contemplated by the present invention that a plungerconstruction be provided in the valve part controlling the magnitude ofthe flow set by a variably regulated orifice and thereby providing aconstant pressure relief. By virtue of the arrangement provided, ahighly responsive flow control valve with linear characteristics issupplied. Moreover, means are thus provided for reducing pump internalback pressure. The flow control system of the present invention affordszero leakage at minimum or maximum line pressures and the flat sidevalve concept provides a valving geometry that is conveniently andeconomically produced in accordance with accepted mass productionfabricating techniques.

The overall pump and valve package also provides a valving structurethat takes less physical space than current commercial side manifoldedvalves thus reducing measurably the axial assembly length of the pumpand valve package and permitting the unit to be advantageously exploitedin cramped quarters.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 4 is an alternative form of apressure part illustrating how a partitioning shoulder may be disposedon the pressure part instead of on the valve part as illustrated in FIG.1;

FIG. 5 is a cross sectional view taken on line V--V of FIG.

FIG. 6 is a view taken on line VI-VI of FIG. 1 and showing onlyadditional details of the valve part, other parts being removed for thesake of clarity;

FIG. 7 is a fragmentary cross sectional view taken on line VIIVII, againwith parts removed but showing additional details of the valve part ofthe present invention; and

FIG. 8 is a fragmentary cross sectional view taken on line Vlll-Vlll ofFIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Although the principles of thepresent invention are of general application, a particularly usefulapplication is made to a power steering pump wherein the output of thepump is regulated as a function of fluid flow. Accordingly, theexemplary structure illustrated herein by means of which the presentinvention may be described constitutes a power steering pump showngenerally at 10 and including a housing 11 having a radial face 12against which is engaged a flange 13 of a generally cup-shaped enclosure14. The enclosure 14 is fastened to the housing 11 by a plurality ofbolts 16.

The housing 11 has an axially extending boss 17 in which is disposed asleeve bearing 18 for joumalling a shaft 19. The usual shaft seal isshown generally at 20 and it will be understood that the shaft 19 can beconnected to any rotational drive, such as the fan belt of an internalcombustion engine in a vehicle.

lnwardly of the enclosure 14 and adjacent the flat surface 12 of thehousing 11 there is provided a stackup of parts constituting apump-Thus, there is provided a first pressure plate member 21, a ringmember 22 and a second pressure plate member indicated at 23. The threeparts 21, 22 and 23 are each appropriately apertured for the purpose ofpassing dowel pins shown at 24 and each of which is threaded intocorresponding recesses 26 formed in the housing 11. Each dowel pin 24has a flange 27 formed thereon which overlies the second pressure plate23. Projecting axially from each respective flange 27 is a pilot portion28 received in corresponding openings 29 of a valve part shown generallyat 30.

Referring to FIG. 2 in conjunction with FIG. I, it will be noted thatthe ring 22 has a double-lobed pumping chamber formed therein as at 31.Rotatable within the pumping chamber 31 is a rotor 32 having a pluralityof generally rectangular notches 33 formed therein each of whichreceives a pumping element 34 which is sized with respect to each notch33 so as to move radially and rock angularly while following theadjoining bore wall of the pumping chamber 31. Each pumping element 34is loaded by a spring 36. It will be noted that the rotor 32 is keyed asat 37 to one end of the shaft 19 which projects beyond the radial wall1-2 into the center opening of the rotor.

Disposed between the valve part 30 and the enclosure 14 is a sealingmember 38- (FIG. 1) thereby dividing the interior of the enclosure 14into a high pressure area 39 and a low pressure area 40. A dischargemember such as a nipple 41 is connected to a radial end wall 42 of theenclosure-14 and has a discharge passage 43 so that high pressure fluidfrom the high pressure zone 39 may be conducted to a point ofutilization, such as a power assisted steering mechanism in a dirigiblevehicle.

The low pressure zone 40 conveniently provides an inlet area for thepump and in this regard, it will be noted that the pressure plate 23 isnotched as at 44,44 as shown in the first and third quadrants in theview of FIG. 3 thereby to communicate inlet fluid into correspondinginlet portions of the double-lobed pumping chamber 31. The notches 44,44also communicate with radially inwardly disposed inlet ports shown at46,46, thereby to assist in filling the space behind the pumpingelements 34 in the notches 33 of the rotor 32.

In the second and fourth quadrants, again using the orientation of FIG.3, it will be noted that the pressure plate 23 has outer discharge ports47,47 and inner discharge ports 48,48, each inner discharge port havinga precompression notch 49 to permit a low rate pressure buildup in thepumping bore between the inlet 44 and the outlet 47.

By virtue of the double-lobed pumping configuration provided by the pump10, it will be appreciated that there are two pumping impulses for eachrotation of the rotor 32 and accordingly, fluid at pump generatedpressure is discharged from the outlet ports 47 and 48.

in accordance with \the principles of the present invention, a flat sidevalve concept is exploited. Thus, the pressure plate 23 constitutes afirst stationary pressure part having a radial face 50. The valve part30 constitutes a movable valve part having a radial face 51. Thus, thetwo confronting relatively movable radial faces or surfaces 50 and 51are formed respectively by the stationary presure part and the movablevalve part.

It, is further contemplated by the present invention that therebeprovided an axially projecting circumferentially continuous shoulder onone of thetwo parts which is disposed between the confronting surfacesthereby to partition the space between the confronting surfaces intoaninlet zone and an outlet zone. In FIG. 1, the axially projectingshoulder is provided at 52 andis formed on the valve part, thereby toprojectaxially from the surface 51 toward the surface 50.

Referring to FIGS. 1, 3 and 6 in conjunction with one another, it willbe noted that the shoulder 52 is circumferentially continuous but is notformed in the shape of a regular circle: Rather, the shoulder 52 isdisposed in a more or less rectangular fashion so that it borders therespective inletand outlet ports 46 and 47, thereby providing an inneroutlet zone 53 and an outer inlet zone 54. Accordingly, all of theoutlet ports 47,47, 48,48 communicate with the outlet zone 53 while thecorresponding inlet ports 44,44, 46,46 communicate with the inlet zone54. That part of the face 51 which is in the outlet zone 53 is shown at53a and the corresponding part of the face 50 is shown at 53b. i

ln practicing the flat side valve concept of the present invention, itwill be readily appreciated by those skilled in the art that the axiallyprojecting shoulder may be reversed and may be situated on thestationary pressure part also. Accordingly, the alternative constructionis shown in FIGS. 4 and wherein a stationarypressure part is shown at230, all of the likeparts being designated by like numbers but with thesuffix a. With such an arrangement, it will be appreciated that thevalve part would be provided :with a flat, radial surface and the radialsurface 50a of the pressure part 23a would be characterized'by theaxially projecting shoulder 52a.

Referring now to FIGS. 6 and 7, additional details of the valve part 30are shown. First of all, the valve part has a centrally disposed boreshown at 60 and which bore intersects the radial surface 51 thereby toprovide a valve seating edge 61 which'forms the edge of an orifice shownat 62.

-Axially inwardly of the orifice 62, the bore 60 has an enlarged annulus63. The bore 60 is successively counterbored as at 64 and 65respectively Slidably mounted within the bore 60 is a plunger showngenerally at 66. The plunger 66 has an outer peripheral surface 67'which includes a tapered valve seat 68 contracting down to a reduceddiameter peripheral surface 69 which is very close in dimension to theinternal diameter of the bore 60. Thus, the tapered valve surface 68cooperates with the valve seating edge 61, thereby to selectively changethe orifice 62 when the plunger 66 is moved relative to the bore 60 andmaking the orifice 62 a variably sized orifice.

- The peripheral surface of the plunger 66 is recessed to receive anO-ring sealing member 70 engageable with the walls of the bore 60. Theplunger 66 terminates in a still further reduced diameter portion 71thereby leaving a radial shoulder 72 against which is seated a backingring 73 bottoming one end of a spring 74. The opposite end of the spring74 is bottomed against a cap member 76 having axially extending sidewalls 77 received in the counterbore 65.

The plunger 66 has a passage extending therethrough which is identifiedat 78. Situated within the passage 78 is a square rod 79. One end of therod 79 engages against the cap member 76 while the other end engagesagainst a ball valve 80. The ball valve 80 is biased by a coil spring 81against a tapered valve seat 82 formed in the passage 78 and theopposite end of the spring 81 is engaged by a retainer disk 83 held inthe end of the plunger 66.

A coil spring .84 engages a rear wall of the valve part and is disposedradially outwardly of the cap 76. A plurality of passages in the form ofcircumferentially spaced apertures are provided at 86 and lead from theannulus 63-to the rear wall 87, which rear wall 87 forms one boundary ofthe pressure discharge area 39 isolated by the sealing member 38.

The recess shown at 88 inwardly of the cap 76 is vented to the inletzone by one or more passages 89 extending through the valve part 30 fromthe recess 88 to a location outwardly of the shoulder 52.

In operation, flow emanating from the pump outlet ports'47 and 48 issuesinto the outlet zone 53. The flow is normally directed through theorifice 62 around the plunger 66'and into the annulus 63 whereupon theflow goes through the passages 86 into the pressure discharge area 39and thence through the nipple fitting 41 and more particularly thepassage 43 formed therein to the outlet line beyond. I

- As pump output flow rises through the orifice 62, the pressure dropacross the orifice 62 increases. The rising dynamic pressure dropreferences an increasing force on the surface 51 while atmosphericpressure prevails on the surface of the rear wall 87. Accordingly, thevalve part 30 moves. open against the spring 84 and achieves apredetermined flow output to the discharge area 39. The magnitude of theflow is set by the orifice size 62 and by the force on the spring 84. I

A restriction anywhere downstream of the orifice 62 will create apressure on the face of the plunger 66 and on the surface correspondingto the end surface thereof. As the pressure rises, the plunger 66 isheld in fixed position by the reaction force developed by the spring 74and the cap member 76 up to the preload value of the spring 74. Anypressure above the setting of the spring 74 causes the plunger 66 tomove in a direction of the applied pressure. Since the square rod 79 isstationary, the movement of the plunger 66 which is sealed by theO-ring70 unseats the ball valve whilesimultaneously effecting a closure of theplunger valve heat seating surface 68 on the valve seating edges 61. Anypressure trapped between the plunger valve head seating surface 68-andthe downstream extremity of a pressure line extending from nipple 41 isunloaded through an orifice 91 which interconnects the passage 86 to thelow pressure recess 88 when the ball valve 80 is unseated by the squarerod 79.

The area 39 rearward of the valve part 30, the passages 86, the annulus63 and the recess 88 and the passage 89 are all connected to atmosphericpressure. Accordingly, the pressure differential between the surface 51and the rear wall 87 results in an opening motion of the valve part 30.In this manner, a constant relief pressure is effected. 7

Referring to the drawings, by-pass from the pump output at high pressurefrom within the outlet zone flows over the axial projecting shoulder 52and over the inlet opening I. The high velocity stream A passes over theshoulder 52 in such a manner as to provide an aspirating area B whichinduces a flow C through a passage P, thereby to achieve a su-'percharging effect. As shown on FIG. 6 taken in conjunction with FIG. 8,the passage P" may be provided on both sides of the valve plate.

Although minor modifications might be suggested by those versed in theart, it should be understood that we wish to 'embody within the scope ofthe patent warranted hereon all such modifications as reasonably andproperly come within the scope of our contribution to the art.

We claim as our invention:

1. A rotatable pump having an axis of rotation comprising, twoconfronting relatively movableradial surfaces formed by a stationarypressure part and a movable valve part, respectively, an axiallyprojecting circumferentially continuous shoulder formed on one of saidparts and disposed between said surfaces to partition the spacetherebetween into an inner outlet zone and an outer inlet zone,

outlet port means in said pressure part for discharging fluid at pumpgenerated pressure into said outlet zone, inlet port means communicatingwith said inlet zone,

means including said valve port forming an orifice through which all ofthe fluid discharged by the pump is directed, thereby to provide apressure drop across said orifice,

said valve part having a rear surface forming one wall of a dischargespace receiving fluid from said orifice and from which fluid is directedto a point of utilization, a separate relief valve carried in said valvepart and operable to close said orifice in response to changes inpressure differential between opposite sides of said valve part, and

control spring means acting on said rear surface of said valve parttogether with said fluid whereby said valve part is selectively moved inresponse to changes in pressure drop across said orifice to separatesaid radical surfaces and by-pass fluid directly across said shoulder tosaid inlet zone.

2. A rotatable pump having an axis of rotation comprising,

a housing having a flat radial surface,

a stack-up of parts comprising a ring forming a pumping chamber and apressure part having outlet port means formed therein,

a rotor in said ring having a notched periphery, pumping element meanscarried in the notched periphery and which pumping element means arefree to move radially and to rock angularly while following the adjacentwall of the pump chamber,

inlet port means communicating with the exterior periphery of saidpressure part,

enclosure means connected to said housing and forming an inlet zonearoundsaid ring and said pressure part,

a movable valve part adjacent said pressure part, a spring between saidenclosure means and said valve part loading said valve part toward saidpressure part,

said valve part and said pressure part having rigid confrontingrelatively movable radial surfaces,

an axially projecting circumferentially continuous shoulder formed onone of said surfaces and normally in contact with the other of saidsurfaces to partition the space therebetween into an inner outlet zonecommunicating with said outlet ports and an outer inlet zonecommunicating with said inlet ports, means including said valve partforming within the confines of said shoulder a variable orifice the sizeof which varies with the pressure drop across the orifice through whichall of the fluid discharged by the pump is directed thereby to produce apressure drop across said orifice, sealing means between said enclosureand said valve part for separating the interior of said enclosure intoan inlet area and a discharge area,

said valve part having a rear surface forming one wall of the dischargearea receiving fluid from the orifice and from which fluid is directedto a point of utilization,

whereby said valve part is selectively moved in response to changes inpressure drop across said orifice to separate said shoulder from theother of said surfaces and by-pass fluid directly across said shoulderfrom said outlet zone to said inlet zone.

3. A rotatable pump having an axis of rotation comprising,

two confronting relatively movable rigid radial surfaces formed by astationary pressure part and a movable valve part, respectively,

an axially projecting circumferentially continuous shoulder formed onone of said surfaces, and normally in contact with said other surface topartition the space therebetween into an inner outlet zone and an outerinlet zone,

outlet port means in said pressure part for discharging fluid at pumpgenerated pressure into said outlet zone,

inlet port means communicating with said inlet zone, means includingsaid movable valve part forming within the confines of said shoulder, avariable orifice, the size of which varies with the pressure drop acrossthe orifice, through which all of the fluid discharged by the pump isdirected, thereby to provide a pressure drop across said orifice,

said movable valve part having a rear surface forming one wall of adischarge space receiving fluid from said orifice and from which fluidis directed to a point of utilization,

and control spring means acting on said rear surface together with saidfluid whereby said movable valve part is selectively moved in responseto changes in the pressure drop across said orifice to vary the size ofsaid orifice and to separate said radial surfaces and by-pass fluiddirectly across said shoulder. 4. In a pump as defined in claim 3, saidvalve part having an inlet opening formed therein outwardly adjacentsaid shoulder so that high velocity flow by-passed across said shoulderand between said radial surfaces will flow over said inlet opening toprovide an aspirating area for inducing the flow of fluid thereinto, anda passage extending from the rear of said valve part to said inletopening through which fluid is aspirated.

5. A rotatable pump having an axis of rotation comprising, twoconfronting relatively movable radial surfaces formed by a stationarypressure part and a movable valve part, respectively,

an axially projecting circumferentially continuous shoulder formed onone of said parts and disposed between said surfaces to partition thespace therebetween into an inner outlet zone and an outer inlet zone,outlet port means in said pressure part for discharging fluid at pumpgenerated pressure into said outlet zone, inlet port means communicatingwith said inlet zone, said valve part having formed therein inwardly ofsaid shoulder an axially extending bore intersecting said radial surfaceto form an annular valve seating edge, said bore having an enlargedannulus formed therein axially inwardly of said valve seating edge,

and said bore terminating in a counterbore, said valve part furtherincluding a rear face outwardly of said counterbore,

a cap member in said counterbore,

a coil spring bottomed at one end against said cap member,

a plunger slidable in said bore and engaging the other end of saidspring, said plunger having a radially tapered valve head surfacecooperable with said valve seating edge to form a variable orifice,

and passage means in said valve part from said annulus to said rearface,

enclosure means forming with said rear face a discharge cavity leadingto a point of utilization,

and spring means between said enclosure means and said rear face wherebysaid valve part is movable in response to changes in the pressure dropacross said orifice.

6. A pump as defined in claim 5 and further characterized by saidplunger having a passage formed therein,

a ball valve in said passage,

a spring loading said ball valve closed and a rod in said passage havingone end engaged against said cap and the other end against said ballvalve, whereby constant relief pressure is effected.

1. A rotatable pump having an axis of rotation comprising, twoconfronting relatively movable radial surfaces formed by a stationarypressure part and a movable valve part, respectively, an axiallyprojecting circumferentially continuous shoulder formed on one of saidparts and disposed between said surfaces to partition the spacetherebetween into an inner outlet zone and an outer inlet zone, outletport means in said pressure part for discharging fluid at pump generatedpressure into said outlet zone, inlet port means communicating with saidinlet zone, means including said valve port forming an orifice throughwhich all of the fluid discharged by the pump is directed, thereby toprovide a pressure drop across said orifice, said valve part having arear surface forming one wall of a discharge space receiving fluid fromsaid orifice and from which fluid is directed to a point of utilization,a separate relief valve carried in said valve part and operable to closesaid orifice in response to changes in pressure differential betweenopposite sides of said valve part, and control spring means acting onsaid rear surface of said valve part together with said fluid wherebysaid valve part is selectively moved in response to changes in pressuredrop across said orifice to separate said radical surfaces and bypassfluid directly across said shoulder to said inlet zone.
 2. A rotatablepump having an axis of rotation comprising, a housing having a flatradial surface, a stack-up of parts comprising a ring forming a pumpingchamber and a pressure part having outlet port means formed therein, arotor in said ring having a notched periphery, pumping element meanscarried in the notched periphery and which pumping element means arefree to move radially and to rock angularly while following the adjacentwall of the pump chamber, inlet port means communicating with theexterior periphery of said pressure part, enclosure means connected tosaid housing and forming an inlet zone around said ring and saidpressure part, a movable valve part adjacent said pressure part, aspring between said enclosure means and said valve part loading saidvalve part toward said pressure part, said valve part and said pressurepart having rigid confronting relatively movable radial surfaces, anaxially projecting circumferentially continuous shoulder formed on oneof said surfaces and normally in contact with the other of said surfacesto partition the space therebetween into an inner outlet zonecommunicating with said outlet ports and an outer inlet zonecommunicating with said inlet ports, means including said valve partforming within the confines of said shoulder a variable orifice the sizeof which varies with the pressure drop across the orifice through whichall of the fluid discharged by the pump is directed thereby to produce apressure drop across said orifice, sealing means between said enclosureand said valve part for separating the interior of said enclosure intoan inlet area and a discharge area, said valve part having a rearsurface forming one wall of the discharge area receiving fluid from theorifice and from which fluid is directed to a point of utilization,whereby said valve part is selectively moved in responSe to changes inpressure drop across said orifice to separate said shoulder from theother of said surfaces and by-pass fluid directly across said shoulderfrom said outlet zone to said inlet zone.
 3. A rotatable pump having anaxis of rotation comprising, two confronting relatively movable rigidradial surfaces formed by a stationary pressure part and a movable valvepart, respectively, an axially projecting circumferentially continuousshoulder formed on one of said surfaces, and normally in contact withsaid other surface to partition the space therebetween into an inneroutlet zone and an outer inlet zone, outlet port means in said pressurepart for discharging fluid at pump generated pressure into said outletzone, inlet port means communicating with said inlet zone, meansincluding said movable valve part forming within the confines of saidshoulder, a variable orifice, the size of which varies with the pressuredrop across the orifice, through which all of the fluid discharged bythe pump is directed, thereby to provide a pressure drop across saidorifice, said movable valve part having a rear surface forming one wallof a discharge space receiving fluid from said orifice and from whichfluid is directed to a point of utilization, and control spring meansacting on said rear surface together with said fluid whereby saidmovable valve part is selectively moved in response to changes in thepressure drop across said orifice to vary the size of said orifice andto separate said radial surfaces and by-pass fluid directly across saidshoulder.
 4. In a pump as defined in claim 3, said valve part having aninlet opening formed therein outwardly adjacent said shoulder so thathigh velocity flow by-passed across said shoulder and between saidradial surfaces will flow over said inlet opening to provide anaspirating area for inducing the flow of fluid thereinto, and a passageextending from the rear of said valve part to said inlet opening throughwhich fluid is aspirated.
 5. A rotatable pump having an axis of rotationcomprising, two confronting relatively movable radial surfaces formed bya stationary pressure part and a movable valve part, respectively, anaxially projecting circumferentially continuous shoulder formed on oneof said parts and disposed between said surfaces to partition the spacetherebetween into an inner outlet zone and an outer inlet zone, outletport means in said pressure part for discharging fluid at pump generatedpressure into said outlet zone, inlet port means communicating with saidinlet zone, said valve part having formed therein inwardly of saidshoulder an axially extending bore intersecting said radial surface toform an annular valve seating edge, said bore having an enlarged annulusformed therein axially inwardly of said valve seating edge, and saidbore terminating in a counterbore, said valve part further including arear face outwardly of said counterbore, a cap member in saidcounterbore, a coil spring bottomed at one end against said cap member,a plunger slidable in said bore and engaging the other end of saidspring, said plunger having a radially tapered valve head surfacecooperable with said valve seating edge to form a variable orifice, andpassage means in said valve part from said annulus to said rear face,enclosure means forming with said rear face a discharge cavity leadingto a point of utilization, and spring means between said enclosure meansand said rear face whereby said valve part is movable in response tochanges in the pressure drop across said orifice.
 6. A pump as definedin claim 5 and further characterized by said plunger having a passageformed therein, a ball valve in said passage, a spring loading said ballvalve closed and a rod in said passage having one end engaged againstsaid cap and the other end against said ball valve, whereby constantrelief pressure is effected.